Aqueous slurries of diperisophthalic acid (DPI) are useful in forming core particles for encapsulated bleaching compositions such as described in U.S. Pat No. 3,494,787 (issued to J. P. Lund and D. R. Nielsen).
DPI has been described as having two different crystal forms defined by characteristic X-ray diffraction powder pattern spacings in U.S. Pat No. 3,880,914 issued to D. R. Nielsen, which disclosure is incorporated herein by reference. Each crystal form of DPI has a symmetry of structure which is usually associated with an external symmetry or "habit." Two habits of DPI have been identified and designated as "tabular" and "acicular." The tabular habit DPI is characterized by a shape having two approximately equal dimensions with the third dimension about one-fifth to one-third the other dimensions. Tabular habit DPI has characteristic X-ray diffraction powder pattern interplanar spacings as follows:
A PA1 9.17 PA1 5.50 PA1 4.21 PA1 3.75 PA1 3.54 PA1 3.26 PA1 3.20 PA1 3.15 PA1 2.44 PA1 2.39 PA1 2.30 PA1 1.97 PA1 1.93 PA1 1.87 PA1 1.84 PA1 1.80 PA1 1.61 PA1 A PA1 8.47 PA1 5.59 PA1 5.33 PA1 4.64 PA1 4.54 PA1 4.23 PA1 3.71 PA1 3.63 PA1 3.46 PA1 3.40 PA1 3.32 PA1 3.24 PA1 3.19 PA1 3.06 PA1 2.82 PA1 2.78 PA1 2.73 PA1 2.68 PA1 2.60 PA1 2.48 PA1 2.40 PA1 2.27 PA1 2.21 PA1 2.16 PA1 2.15
with major line intensities at interplanar spacings of 4.21, 3.20and 2.39 A. This habit is in contrast to the acicular (needlelike) habit DPI crystal having a typical length to diameter ratio of over 20 and characteristic X-ray diffraction powder pattern interplanar spacings as follows:
with major line intensities at interplanar spacings of 5.59, 4.23 and 3.66 A.
Practical differences reside in the use of aqueous DPI slurries having acicular or tabular crystal habit. The acicular habit crystal as a consequence of its geometry has a tendency to compact or "set-up" in a water slurry with the result that it promotes stoppages in pumps, transfer lines, and related equipment. In contrast to the acicular crystal, an aqueous slurry of tabular habit DPI is pumped and hydraulically transported with relative ease.
U.S. Pat. No. 3,655,738(issued to D. R. Nielsen) describes (Example 3) a process of reacting isophthalic acid and hydrogen peroxide in methanesulfonic acid, cooling the reaction medium to 40.degree. C., centrifuging to separate solid DPI product and water washing the product to give tabular form DPI product having the associated tabular habit external crystal shape. It is desirable to prepare tabular habit DPI/water mixtures without the necessity of using a specific synthesis method. In particular, the metastable nature of aqueous slurries of tabular habit DPI make it desirable to devise a method of easily converting acicular habit DPI/water mixtures into tabular habit DPI/water mixtures.